Larry Gagosian Buys and Sells Buildings the Same Way He Does Art—Behind Closed Doors; If he wasn't dealing art, "I’d probably be in real estate."

While The Observer would never attempt to divine what goes on in Larry Gagosian’s head, based on discussions with real estate and art world experts, it is quite possible the Harkness Mansion could serve, in some capacity, as gallery, showroom, salon.

“The answer is, yes, it’s been done,” an attorney who specializes in zoning told The Observer. “It’s a residential district, which precludes any commercial use, but there is nothing stopping him from putting a gallery in the first few floors.”

The mansion’s cavernous 20,000 square feet could not be entirely given over to art, because the Department of Buildings still requires certain amenities for a residential building to get its certificate of occupancy. In this case, that includes a kitchen and at least one bedroom. The residences could occupy a few floors, or be nothing much more than a garret in the sixth-floor attic.

There are still further restrictions on a gallery conversion. There can be no separate entrances for the home and the gallery and no signage on the doors. Business hours are strictly forbidden—this is not a venue for public viewings. “But that doesn’t mean you couldn’t throw a party there every night if you wanted,” said the attorney.

The stately house would be a nice addition to the 11-gallery Gagosian empire, his most upscale space so far. Yet Mr. Gagosian would not want to go abandoning the mothership at 980 Madison, either. The biggest restriction of all is that no commercial activity could take place in the home. Even for the notoriously behind-closed-doors Mr. Gagosian, the convenience of going around the corner to sign over art would be essential.

Galleries in townhouses on quiet Upper East Side streets are nothing new. L&M Arts operates one, as does Marianne Boesky. Unlike Mr. Gagosian’s new manse, both are partly zoned for commercial use. In Ms. Boesky’s case, it was a doctor’s office on the ground floor that was converted to a gallery in 1971, according to city records. Still, this did not keep her from staging the “dwelling” show in the spring, occupying every floor of the brownstone. Just because it’s a bedroom does not mean it cannot also become a gallery space.

Allan Stone lived over the shop on East 90th Street for 16 years until his death in 2006. The converted firehouse was sold this summer for $9.875 million and is reportedly being turned back into a single-family home. Richard Feigen’s gallery is located on the first few floors of his home, but any sales must be done off-site due to the aforementioned residential restrictions.

Perhaps the best known—if most notorious—example of a gallery inside an Upper East Side mansion was the $150,000-a-month 71st Street palace that another Larry once occupied. The disgraced Salander O’Reilly, at 22 East 71st Street, actually lay within a commercial district, making sales there legit. Well, legit from a zoning perspective.